Metered aerosol dispensing valves have been used in many devices and are well known in the art. Metered aerosol dispensing valves have been disclosed in a number of references. Examples include: U.S. Pat. No. 4,506,803, issued Mar. 26, 1985 to Franklin et al.; U.S. Pat. No. 4,142,652, issued Mar. 6, 1979 to Platt; U.S. Pat. No. 4,819.834, issued Apr. 11, 1989 to Thiel; U.S. Pat. No 5,421,492, issued Jun. 6, 1995 to Barger et al.; and U.S. Pat. No. 3,974,941, issued Aug. 17, 1976 to Mettler.
One particularly important use of metered aerosol dispensing valves is in the dispensing of aerosolized active agents, one example being a medicament. When dispensing aerosolized medicaments the quantity of the dispensed dose is of critical significance. Many medicaments have narrow therapeutic windows requiring the quantity of each dispensed dose to fall within specific circumscribed limits.
Another important consideration encountered with the metered dispensing of aerosolized medicaments is the medium within which the medicament is contained. Many aerosolized medicaments are in a fluid-like medium: a solution, suspension or emulsion. These fluid-like or liquid formulations contain one or more excipients such as lubricants, surfactants, diluents and propellants. One example of such an aerosol drug formulation is described in U.S. Pat. No. 5,126,123, issued Jun. 30, 1992 to Johnson, and incorporated herein by reference. In an effort to avoid exposing patients to non-necessary excipients and in an effort to use environmentally friendly or "green" propellants, formulations containing only a non-chlorofluorocarbon propellant and an active agent (a "two-component-formulation") are particularly attractive. An example of a two-component formulation is described in WO 93/11743, published Jun. 24, 1993, in the name of Glaxo Group Limited and incorporated herein by reference.
Medicaments contained in an emulsion or suspension require frequent mixing to aid in keeping the combination of medicament and the other components of the formulation in a homogenous state, preventing the settling of a suspension or the separation of an emulsion. However, many prior art metered aerosol dispensing valves sequester a single dose within a metering chamber or bottle emptying device, secluding this single, next-to-be-used dose, from the reservoir containing the medicament supply. This sequestering prevents any applied mixing energy from homogeneously blending the medicament within the metering chamber with the remaining medicament supply contained within the reservoir. An example of this prior design can be found in U.S. Pat. No. 4,142,652, issued Mar. 6, 1979 to Platt. These prior art valve designs, when utilized with medicaments in a suspended, emulsified or other than solution form, result, many times, in aerosolized doses or "shots" that expel either a greater or lesser quantity of medicament compared to the specific quantity required. Manufacturers of aerosolized medicaments are additionally facing pressures to eliminate the use of chlorofluorocarbon ("CFC") containing propellants. Manufacturers are therefore looking for valves that are not only highly accurate, but valves that are compatible with the new non-CFC propellants.
It is therefore an object of the present invention to define and delineate a metered aerosol dispensing apparatus, more particularly an aerosol dispensing valve, incorporating a controlled metered dispensing function having a flow-through metering chamber allowing the formulation or composition within the metering chamber and the reservoir to mix when agitated. It is also an object of this invention to provide a homogenous mixture of the active agent within the metering chamber and reservoir; yielding aerosolized doses that have a consistent and constant dosing profile. It is further an object of this Invention to provide a aerosol dispensing valve that is fully compatible and highly accurate when utilized to dispense a medicament with a non-CFC propellant whether in a two-component formulation or when containing a greater number of excipients. These objects and further objects will become evident from the description of the invention below.